This invention relates to the field of liquid catalysts and more particularly to liquid catalysts capable of cross-linking amino resins.
Amino resins are used in the area of wood products including particleboard, hardwood, plywood, decorative laminate, furniture assembly, etc. Amino resins are supplied in liquid form and are combined with a catalyst at the time of use to form an adhesive substance that is applied to the wood product. This adhesive substance provides adhesion between wood surfaces.
The catalysts are either acidic substances or other materials capable of liberating free acid upon addition to the amino resin. The acidic property of the catalyst promotes cross-linking amino resins and accordingly, the cross-linking or setting of the adhesive substance so that the adhesive substance has the necessary high strength, water resistance and cold flow resistance in order to meet its necessary applications. For example, hardwood floors used for flooring in truck trailer, truck bodies and shipping containers are laminated using a catalyst/amino resin with high strength cross-linking. The quality of lamination can then be verified using Fruehauf Engineering Standards, with one of the most important criteria being the wet shear strength.
The amount and type of catalyst used determines whether the adhesive bond can be cured at room temperature or at higher temperatures. Cure time may vary from a few minutes at high temperatures to a few hours at room temperature. In an application where high frequency heating is required, as for example with laminated pieces of wood flooring, it is common to reduce the time required to cure the adhesive substance.
Current catalysts used in combination with amino resins are in powder form.
A major drawback with a powder catalyst is that powders are not easy to manipulate. Mass transfer of powder materials requires special equipment and/or more human manipulations.
Also, powder catalysts pose certain problems in terms of dust formation during transfer, which may cause toxic effects on humans (irritating mucous membranes and upper respiratory tract).
Care must always be taken to mix homogeneously the blend of powder catalyst and liquid amino resin to avoid any lumping of powder, which will cause a bum or an arc if high frequency heating is used.
While the use of a high level of powder catalyst imparts lower setting time, the amount of powder catalyst mixed with the amino resin is limited to about a maximum of 15% by weight. Increasing the amount of powder catalyst above 15% by weight increases the viscosity and reduces the pot life of the mixture, but decreases the adhesivity and strength of the mixture. Moreover, powder catalysts do not contribute any adhesive property to the mixture and a higher concentration of powder catalyst reduces the relative amount of amino resin in the mixture and therefore reduces the adhesive performance of the resulting mixture.
When properly cured, the resulting bond of the amino resin cross-linked with a powder catalyst is hard and brittle and is characterized by a low impact strength and low elongation point prior to breakage.
Accordingly, there remains a need to develop a catalyst that is commercially beneficial for the wood glue industries and which can be easily mixed at a relatively high concentration with a liquid amino resin to provide a resulting adhesive substance with an adequate viscosity, pot life, and setting time. There also remains a need to provide a catalyst that reduces the cycle time of a high frequency heating press, while contributing adhesive properties to the final adhesive substance.
It is an object of one aspect of the present invention to provide a catalyst with improved adhesive properties and flexibility.
It is a further object of one aspect of the present invention to provide a catalyst with improved cross-linking capabilities and properties that facilitate mixing with an amino resin.
According to one aspect of the present invention, there is provided a liquid catalyst for cross-linking an amino resin, said liquid catalyst comprising between 52 and 98% copolymer, between 3 and 14% acid and between 4 and 14% ammonium salt.
In a preferred embodiment of the present invention, the liquid catalyst has several advantages over currently used powder catalysts, some of which are the following. The liquid catalyst has a relatively low viscosity that allows it to be easily transferred and mixed with an amino resin. The liquid catalyst provides a fast curing time when cured with high frequency heating. It provides a flexible glue line with high impact strength and a high elongation point. The liquid catalyst provides adhesive properties to the catalyst/amino resin mixture and it provides excellent bond strength and excellent water resistance to the adhesive substance.